Modulator apparatus utilizing piezoelectric plates

ABSTRACT

A modulator and method for providing uniform increments of fluid in a continuously pulsing manner, is disclosed. The modulator employs the piezoelectric effect to impart peristaltic-like action to a flexible, resilient channel causing fluid contained within that channel to be pulsed from the channel, in the form of substantially uniform increments or slugs. The modulator is employed, for example, in combination with, and to feed fluid sample to, an analytical instrument such as a flame spectrophotometer.

United States Patent 1 Mossotti et al.

Oct. 2, 1973 1 MODULATOR APPARATUS UTILIZING PIEZOELECTRIC PLATESInventors: Victor G. Mossotti; Judith A. Eakin,

both of Urbana, Ill.

[73] Assignee: University of Illinois Foundation,

Urbana, Ill.

[22] Filed: Aug. 5, 1970 [21] Appl. No.: 61,148

[52] US. Cl 3I0/8.3, 310/86, 356/36,

356/87, 356/187 [51] Int. Cl I-I04r 17/00 [58] Field of Search 310/8,8.1, 9, 9.6,

[56] References Cited UNITED STATES PATENTS 2,902,251 9/1959 Oncley3lO/8.l X

3,150,592 9/1964 Stec 310/8 X OTHER PUBLICATIONS Herrmann: FreseniusZeitschrift Fuer Analytische Chemie, Band 212, Heft 1, 1965 pages I and12-14.

Mavrodineanu: Spectrochimica Acta, Vol. 17, 1961 pages 1016, 1022 and1023.

Neu et al.: Messtechnik, July 1968, pages 154-159.

Primary ExaminerDavid Schonberg Assistant ExaminerF. L. EvansAttorney-Merriam, Marshall, Shapiro & Klose [57] ABSTRACT A modulatorand method for providing uniform increments of fluid in a continuouslypulsing manner, is disclosed. The modulator employs the piezoelectriceffect to impart peristaltic-like action to a flexible, resilientchannel causing fluid contained within that channel to be pulsed fromthe channel, in the form of substantially uniform increments or slugs.The modulator is employed, for example, in combination with, and to feedfluid sample to, an analytical instrument such as a flamespectrophotometer.

6 Claims, 3 Drawing Figures i sm PATENTED 21975 3.763.385

SHEET 10F 2 INVENTO RS k'ciw/ %QQ&ZZZ

ATTORNEYS RECOVERY OF 2852A EMBSSBON SPECTROGRAM "B" SPECTROGRAM "A"INVENTORS ATTORNEYS MODULATOR APPARATUS UTILIZING PIEZOELECTRIC PLATESThe present invention relates to a modulator for imparting certain flowcharacteristics to fluid materials. In general, it concerns an apparatusand a method for providing uniform increments of fluid materials, to beused for example in feeding fluid samples to an analytical instrumentsuch as a flame spectrophotometer. More particularly, it involves anapparatus and a method which employ the piezoelectric effect to produceperistaltic action in a channel containing a fluid material whichperistaltic action propels or injects, in a highly reproducible manner,the fluid material from the channel in the form of uniform increments orslugs.

Analytical instruments suitable for use in detecting or determining theamount of a component, i.e., analyte, present in a fluid sample are wellknown. Such instruments include flame spectrophotometers, plasma jets,gas chromatographs, and the like. These analytical instruments allrequire some means or device for feeding the fluid sample to be analyzedinto the analyzing element of the analytical instrument. For example,commercial flame spectrophotometers generally employ atomizers tointroduce a liquid sample to be analyzed into a flame. Such atomizersare designed based upon the important objective that the liquid samplebe introduced into the flame at a stable and reproducible rate. Inpractice, however, changes or fluctuations in sample aspiration rateoccur. Such fluctuations in the rate at which sample is aspirated intothe flame, especially in view of the numerous other changes orfluctuations which occur at other points in the analytical process,adversely effect the reproducibility of the analytical measurementwhich, of course, limits the quantitative accuracy of the analyticalinstrument.

The present invention provides an apparatus as well as a method forsupplying or feeding a fluid sample to an analytical instrument such asa flame spectrophotometer, in such a manner that the sensitivity anddetection limits of the analytical instrument are markedly improved.

In general, the apparatus of the present invention is a' modulator whichemploys a piezoelectric sandwich comprising at least two piezoelectriccrystals or plates and a flexible, resilient channel partiallysandwiched between the plates.

Piezoelectric materials are well known and per se do not form the basisof the present invention. Piezoelectric materials are materials whichwhen subjected to an applied voltage generate a stress in the crystalsof the material causing the material to deform. For example, when such amaterial is subjected to an alternating current (AC) voltage, it willoscillate with a frequency and amplitude proportional to the applied ACvoltage. The present invention relies upon this piezoelectric effect toimpart a peristaltic-like action to a flexible resilient channel.

When a flexible, resilient channel for example a latex tube, is placedbetween two piezoelectric plates and an AC voltage applied to theplates, the plates deform in a manner which imparts wave-likecontractions to the latex tube, thereby propelling and continuouslypulsing fluid-material contained in the tube through the tube and out ofthe tube. The fluid material leaving the tube is in the form of uniformincrements.

The present invention will be better understood by reference to theaccompanying drawings in which:

FIG. l is an end view in partial cross section of a single channelmodulator of the present invention attached to a black box" which maybe, for example, an analytical instrument; and

FIG. 2 is a perspective view in partial cross sectiori of a dual channelmodulator of the present invention attached to a dual capillary totalconsumption burner suitable for use in flame spectrophotometry; and

FIG. 3 is a graphic illustration comparing two spectrograms, spectrogramA resulting from use of the present invention and spectrogram Bresulting from conventional practice.

Referring to FIG. ii, there is shown a single channel modulator 30 ofthe present invention threadably attached to a black box 31. Themodulator 30 is used to supply uniform increments of fluid material tobox 31.

Single channel modulator 30 comprises a conduit or channel 32, theintermediate portion of which is positioned, i.e., sandwiched, between apair of piezoelectric plates, i.e., first piezoelectric plate 34 andsecond piezoelectric plate 35. A frame or support 33 provides means forsupporting, holding and positioning the sandwiched= channel. Channel 32has an inlet 50, an outlet 51 and consists of a flexible, resilientmaterial, for example, a latex tube having an inside diameter of onethirty-second of an inch and a wall thickness of one sixty-fourth of aninch. The outlet 51 of channel 32 is provided with a capillary 36 orother means suitable for providing a passageway for fluid materialleaving channel 32 to enter box 31 through inlet port 42. Piezoelectricplates 34 and 35 are each provided, respectively, with a pair ofelectric contacts 37a37b and 38a38b. Electric contacts 37a-37b and380-38b are attached to an AC power source (not shown). Any suitable ACpower source may be employed. One suitable AC power source which hasbeen found useful produces a volt, 35 cycles per second signal.

A portion of channel 32 located between the inlet 50 and theintermediate (sandwiched) portion is partially restricted by means offlow restrictors 39 and 40. These flow restrictors offer resistance tothe flow of fluid material and thus when an increment, or slug, or fluidis subjected to peristaltic-like action in the intermediate (sandwiched)portion of channel 32, the increment tends to exit from channel 32 intocapillary 36, and then into box 31 via inlet port 42. Support 33 isprovided with means such as positioning support screws 43, 44, 415 and46 for holding and positioning the sandwiched channel.

The operation of the single channel modulator shown in FIG. ll will nowbe described with reference to an application where black box 311 is ananalytical instrument. In such an application the modulator is used tosupply a liquid or gas sample from a reservoir (not shown) into ananalytical instrument where the fluid sample is analyzed to determinethe quantity of a component, i.e., analyte, contained in the sample. Thesingle channel modulator feeds or injects fluid sample into theanalytical instrument in a continuously pulsing manner. It alsointroduces the fluid sample into the analytical instrument inreproducibly uniform increments. Thus, the flow of fluid sample fromthe. single channel modulator into the analytical instrument may becharacterized as a continuous pulsing of uniform in- I crements or slugsof sample. The advantages of feeding fluid samples to certain analyticalinstruments in such a manner will be exemplified and further describedhereafter.

FIG. 2 shows another embodiment of the present invention wherein a dualchannel modulator 1 of the present invention is attached to a dualcapillary total consumption burner 2 which may be employed as the burnerin a flame spectrophotometer.

The dual channel modulator 1 comprises a three layer piezoelectricsandwich mounted in a frame or support 6. Piezoelectric sandwich 5comprises first channel 3 and second channel 4 and piezoelectric plates7, 8 and 9. An intermediate portion of channel 4 is disposed(sandwiched) between first piezoelectric plate 7 and secondpiezoelectric plate 8 and channel 3 is similarly disposed between secondpiezoelectric plate 8 and third peizoelectric plate 9. Piezoelectricplates 7, 8 and 9 are provided with suitable electric contacts (notshown) for applying an AC voltage to the plates. The outlet ends ofchannels 3 and 4 are provided, respectively, with first capillary 11 andsecond capillary l0. Piezoelectric sandwich 5 is positioned and securedwithin support 6 by means of positioning support screws l2, l3, l4 and15. Spacer members 16 and 17 prevent piezoelectric plates 7, 8 and 9from making physical contact with each other.

Dual capillary total consumption burner 2 is provided with inlet ports20 and 21 to permit support gases such as fuel and air or oxygen toenter the burner.

As mentioned above, in the embodiment illustrated in FIG. 2, the dualchannel modulator of the present invention is used to feed a fluidsample to the burner of a flame spectrophotometer. Flamespectrophotometers are analytical instruments which are often employedto determine the quantity of a metallic element present, for example, asan impurity, in a liquid sample. One of the main components of a flamespectrophotometer is a burner, such as the dual capillary totalconsumption burner illustrated in FIG. 2. The burner, when supplied withsupport gases should, under optimum conditions, produce a steady flame.The sample to be analyzed is prepared in a fluid state and introducedunder conditions controlled as nearly as possible into the flame causinga characteristic radiation from the flame. The characteristic radiationfrom the flame is collected, rendered monochromatic and focused by anoptical system (not shown) onto a photosensitive detector (not shown).The intensity of the isolated radiation striking the photosensitivedetector is indicated, and generally recorded, by a meter (not shown).

Operation of the dual channel modulator illustrated in FIG. 2 as it isused to supply a fluid sample to the dual capillary total consumptionburner will now be described.

Before voltage is applied to the piezoelectric sandwich 5, both channels3 and 4 of the modulator 1 are slightly compressed by means ofpositioning support screws l2, l3, l4 and 15.

Support gases are fed to the burner 2 through inlets 20 and 21 andignited at the outlet of the burner nozzle. Either channel 3 or channel4 is fed with a liquid containing solvent and the component, i.e.,analyte, of analytical interest and the other channel is fed with puresolvent. The natural aspiration of the burner causes these liquids to bedrawn up into channels 3 and 4. At this point, an alternating currentvoltage, for example a [00 volt, 35 cycles per second signal is appliedto the piezoelectric sandwich 5. During the first half cycle after thevoltage is applied, the three layer piezoelectric sandwich 5mechanically warps filling one channel, e.g., channel 3, with anadditional quantity of fluid while simultaneously forcing or injectingan incremental volume of fluid out of the other channel, i.e., channel4, into and through capillary tube 10 and into the flame. During thesecond half cycle after voltage is applied, the peristaltic-like actionof channels 3 and 4 reverse. After a stabilization cycle, the describedaction results in a modulation of the analyte introduced into the flamewhile the net solvent injection rate remains constant and unmodulated.

Some of the practical advantages of employing a modulator of the presentinvention in flame spectrophotometry will now be described.

The dual channel modulator and the dual capillary total consumptionburner illustrated in FIG. 2 were used, as described, in a flamespectrophotometer. The fluid analyzed was a percent ethanol solutioncontaining 2ppm of magnesium (Mg). The support gases for the burnercomprised premixed acetylene and nitrous oxide. The results of theanalysis were recorded as spectrograms and these spectrograms werecompared with spectrograms obtained from other analyses wherein the sameburner, support gases and conditions were employed to analyze samples ofthe same fluid fed to the burner in a conventional manner, viz, byaspiration through capillaries. FIG. 3 illustrates spectrogramsrepresentative of those obtained. As is apparent from FIG. 3, theinterpretation of spectrogram A (resulting from use of the presentinvention) is vastly simplified as compared to spectrogram B (resultingfrom conventional practice). In addition, the analytical sensitivitiesand detection limits of the instrument were markedly improved by use ofthe present invention, as evidenced by the substantially improved signalto noise ratio.

While the present invention has been described, in part, with referenceto analytical instruments, and more particularly in reference to flamespectrophotometers, it is apparent that the modulator of the presentinvention will have utility in other applications where uniformincrements of fluid materials need be supplied in a continuously pulsingmanner. For example, the modulator may find utility in various fuelsupply applications and the like. Modifications of the inventionapparent to those skilled in the art are intended to be within thespirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A modulator for providing uniform increments of fluid material, saidmodulator comprising at least two piezoelectric plates, at least oneflexible, resilient tube means positioned so that an intermediateportion of said tube means is interposed between said plates, supportmeans for positioning and holding said plates, said plates beingpositioned and supported so that peristaltic-like action can be impartedto said tube means when AC voltage is applied to said plates.

2. The modulator of claim 1 wherein said flexible, resilient tube meansis a latex tube.

3. The modulator of claim 1 wherein the inlet portion of said tube meansis provided with a partial flow restriction.

4. The modulator of claim 1 wherein the outlet portion of said tubemeans is provided with conduit means, said outlet portion being nototherwise restricted.

plates, said modulator being adapted to impart a peristaltic-like actionto said flexible, resilient tube when an AC voltage is applied to saidplates, whereby when fluid material enters the inlet end of said tube,uniform increments of said fluid material are provided at the outlet endof said tube.

I t I t t

1. A modulator for providing uniform increments of fluid material, saidmodulator comprising at least two piezoelectric plates, at least oneflexible, resilient tube means positioned so that an intermediateportion of said tube means is interposed between said plates, supportmeans for positioning and holding said plates, said plates beingpositioned and supported so that peristaltic-like action can be impartedto said tube means when AC voltage is applied to said plates.
 2. Themodulator of claim 1 wherein said flexible, resilient tube means is alatex tube.
 3. The modulator of claim 1 wherein the inlet portion ofsaid tube means is provided with a partial flow restriction.
 4. Themodulator of claim 1 wherein the outlet portion of said tube means isprovided with conduit means, said outlet portion being not otherwiserestricted.
 5. The modulator of claim 1 comprising three piezoelectricplates and two flexible, resilient, tubes.
 6. A single channel modulatorfor providing, in a continuously pulsing manner, increments of fluidmaterial, said modulator comprising a pair of piezoelectric plates, aflexible, resilient tube positioned so that an intermediate portion ofsaid tube is interposed between said plates, means for applying an ACvoltage to said plates, said modulator being adapted to impart aperistaltic-like action to said flexible, resilient tube when an ACvoltage is applied to said plates, whereby when fluid material entersthe inlet end of said tube, uniform increments of said fluid materialare provided at the outlet end of said tube.